Print systems include presentation architectures that are provided for representing documents in a data format that is independent of the methods that are utilized to capture or create those documents. Examples of presentation systems (or Page Description Languages (PDLs)) include Portable Document Format (PDF) and PostScript (PS). According to these systems, documents may include mixed content data objects.
Image transforms perform a rasterization to transform a PDL or Image Data Format (e.g., Tagged Image File Format (TIFF) or Joint Photographic Experts Group (JPEG)) data stream into a raster bit plane for each colorant produced by a device. In a PDL, the mixed content data objects include text, image, graphics, smooth shades and blended transparent regions. Thus, it is desirable to identify the object type of each pixel in the raster bit plane to perform post rasterization functions, such as selective screening per object type.
Typically, the object type information is stored in a separate bit-plane, referred to as the Tagged Object Bit-plane. The Tagged Object Bit-plane is a 2-bit per pixel bit-plane where four object types (image, text, graphics and smooth shade) can be identified. The Tagged Object Bit-plane is generated during rasterization. However, a problem is encountered during generation in that types are applied using either a Separation or DeviceN color space, and individual colorant Tagged Object Bit-planes may have different object types for each colorant.
For example, for an image described using DeviceCMYK at a cyan, magenta, yellow and black (CMYK) output device, all of the pixels describing the image in all four colorants may be marked as having an object type of Image. However, if a text object having a Separation/Magenta color space is applied on top of the image with overprinting enabled, only the pixels in the Magenta Tagged Object Bit-plane will be marked as Text; while the Cyan, Yellow and Black Tagged Object Bit-planes remain as Image. This results in ambiguity as to the correct object type for certain pixels when all four Tagged Object Bit-planes are processed.
Accordingly, a mechanism to accurately identify objects during generation of Tagged Object Bit-planes is desired.